Method of casting parts of high melting point metal in molds

ABSTRACT

A method of die casting, particularly of metals with high melting points including iron and steel, characterized by inserting in the cavity of each die a pasteboard form prefabricated in the shape of the respective cavity and containing a refractory substance, then closing the mold and casting the metal part in the usual manner. Where desired, localized tempering of the part being cast may be obtained by reducing the thickness of the prefabricated pasteboard form in that region, and conversely, soft regions may be provided by reinforcing the thickness of the forms in those locations.

United States Patent Lefebvre Sept. 16, 1975 [54] METHOD OF CASTING PARTS OF HIGH 3,266,099 8/1966 Bucy 164/305 X 3,472,308 10/1969 Lauth t 164/125 X 3,528.478 9 1970 Koch et al. ..164/1l3 [75] Inventor: Jean Henri Lefebvre, Chaville,

France [73] Assignce: Regie Nationale des Usines Renault,

Boulogne-Billancourt. France [221 Filed: Feb. 12, 1974 {211 Appl. No.: 441,744

[30] Foreign Application Priority Data Feb, 13, 1973 France 73.05064 [52] US. Cl. 164/72; 164/113; 164/126 [51] Int. Cl. B22D 27/04 [581 Field of Search 164/72, 113, 125, 126, 164/267, 305

[56] References Cited UNlTED STATES PATENTS 1,994,634 3/1935 Broughton 164/125 X 2,757,426 8/1956 Brennan 164/23 Primary Examiner-Francis S. Husar Assistant ExaminerJohn E. Roethel Attorney, Agent, or FirmOblon, Fisher, Spivak, McClelland & Maier 5 7 1 ABSTRACT A method of die casting, particularly of metals with high melting points including iron and steel, characterized by inserting in the cavity of each die a pasteboard form prefabricated in the shape of the respective cavity and containing a refractory substance, then closing the mold and casting the metal part in the usual manner. Where desired, localized tempering of the part being cast may be obtained by reducing the thickness of the prefabricated pasteboard form in that region, and conversely, soft regions may be provided by reinforcing the thickness of the forms in those locations.

10 Claims, 2 Drawing Figures METHOD OF CASTING PARTS OF HIGH MELTING POINT METAL IN MOLDS BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to the die casting of metals, and more particularly concerns an improved method of die casting metals and especially such metals having high melting points, such as cast iron and steel, but also which can be used with other metals, such as aluminum, bronze and alloys of copper.

2. Description of the Prior Art Conventionally, the dies used in such metal casting, some of which have been cooled. are coated with various materials having different degrees of insulating characteristics. However, such die casting in the past has suffered from several disadvantages, of which the principal ones are the poor durability of the dies thereby resulting in rapid discard of the molds, the difficulty experienced in stripping the molds and, in the casting of ferrous metals, the possibility of carbide formation. Reduction of the possibility of such carbide formation, in the case of cast iron, has been obtained by applying a coat of lampblack to the surface of the mold with an acetylene torch. Additionally, in the past, it has been found to be somewhat difficult to properly set certain coatings in place within the mold, such as, for example, by use of a plasma torch.

SUMMARY OF THE IVNENTION Accordingly, it is an object of the present invention to provide an improved method of die casting which will make the stripping of the molds relatively simple.

Another object of the present invention is to provide a method of casting parts of metals, particularly those having high melting points, in molds which will result in increased durability of the molds being used therein.

Still another object of this invention is to provide an improved method of casting parts of metals, particu larly those having high melting points such as certain ferrous metals wherein carbide formation is substantially precluded.

Yet another object of this invention is to provide an improved method of coating the molds used in the die casting of parts from high melting point metals.

The foregoing and other objects are achieved according to at least one aspect of the present invention by replacing the classical coating heretofore generally employed with a pasteboard member formed of cellulose or other fibrous material, which may be impregnated with a refractory material of a thickness and porosity suited to the particular problem at hand, particularly to the nature of the metal being cast, and conforming to the shape and massiveness of the part being cast, or in other words, to the shape of the die cavity or imprint. The refractory substance can also simply be applied over the layer of pasteboard by spraying or dipping. This pasteboard member is formed according to the customary processes of pasteboard manufacture and is remolded in each die.

The use of these forms of pasteboard permits reduction of the investment in molds by virtue of the fact that the time of immobilization of the molds, due to the usual coating operations heretofore employed, is replaced here by the simple insertion in the dies of separately prefabricated forms. Moreover, the inherent insulating ability of pasteboard makes it possible to improve the quality of the castings, along with improving the endurance of the dies, by reducing the effects of surface thermal shock thereon and preventing diffusion effects at the contact with the cast metal.

It further is readily possible to produce local variations in the structure of the cast parts by merely varying the pasteboard thickness where desired. For example, localized tempering can be obtained by reducing the thickness of the pasteboard by removing some of it by providing perforations in certain regions of the pasteboard form, the corresponding part of the die being preferably cooled. Conversely, it is possible to increase the thickness of the pasteboard form in some places by providing filters and suction at corresponding parts of the die to evacuate the gas resulting from combustion of the pasteboard, in order to prevent the formation of blowholes in the parts.

This local reinforcement of the insulation can be used either to secure specialy annealed zones in massive pieces or more generally to permit molding of very thin pieces while maintaining a normal structure therein, which particularly is useful in the case of cast iron.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects, features and attendant advantages of the present invention will be more fully appreciated as the same becomes better understood from the following detailed description when considered in connection with the accompanying drawing, in which like reference numerals designate like or corresponding parts throughout the several views, and wherein:

FIG. 1 is a longitudinal cross-section view of a camshaft mold; and

FIG. 2 is a cross-sectional view taken along the line Il-Il of FIG. 1.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Referring now to the drawing, an upper metal die 1 and a lower metal die 2 of a mold for die casting camshafts of steel or cast iron are shown meeting along a joining plane 3, wherein each of the metal dies has an imprint of a form appropriate to that of the part to be cast, which in the present case is a camshaft.

In conformity with the present invention, coating of the interior surfaces of the cavities according to heretofore conventional practice is replaced by the simple introduction into each of the mold cavities of an inlaid contact layer previously fabricated in the exact shape of the cavity from a pasteboard material. Quite common pasteboard can be used, for example, gray pasteboard of 0.2 to 0.5 millimeters in thickness. This pasteboard can be impregnated with a refractory material or more simply covered or soaked with such refractory material by spraying or dipping. The refractory substance can, for example, be that heretofore used for coating dies.

The pasteboard is shaped by the usual methods of the industry so as to form the two linings 4 such that they assume the exact shapes of interiors of the mold cavities, with a peripheral border 5 being provided projecting out in the joining plane 3.

Placing these linings in the dies is done very quickly, which consequently reduces the time of immobilization of the molds and, therefore, the number of molds necessary to maintain a given production rate. When the mold is reclosed, the two linings 4 of the two dies 1 and 2 are squeezed together at their borders 5 in the joining plane 3, which holds them in place and assures effective sealing.

When the molten metal, which can be one having a high melting point, such as steel or cast iron, is poured. the liquid metal coming into contact with the pasteboard causes combustion of the latter, but the refractory materials with which the pasteboard has been covered or impregnated is instantly fritted by the heat of the metal and serves in turn as the support for the burned pasteboard residues so that they are not entrained by the flow of the metal.

The insulating characteristic of the pasteboard considerably slows the thermal exchange between the casting and the die, so that the casting, by not being cooled too rapidly, is of improved quality, and at the same time the durability of the die is equally improved by reduction of the superficial thermal shock and suppression of diffusion phenomena at the contact of the metal being cast, since this contact is itself eliminated. Finally, the casting, once solidified, is much easier to strip from the moldv Still, if it is desired, one can reduce or eliminate the insulating character of the linings 4 in certain places in order to obtain a localized tempering effect, such as the example illustrated, to temper bosses 6 of the camshaft cams, by simply cutting a window in the pasteboard so that the metal can therethrough come into direct contact with the die. At the same time, in order to emphasize this tempering effect and improve the durability of the die, a cooling system is preferably provided for the region facing this window, being shown here as liquid cooling zones 7. In this way, after cooling, the casting has a much greater surface hardness at the locations of the bosses 6 of the cams, while remaining annealed everywhere else, particularly along the axis and in the bearings 8 of the camshaft.

Conversely it is possible to produce specially soft re gions at certain locations of the casting, where desired, notably at the part indicated by the reference numeral 9 which is to have teeth cut therein to form the gear for driving the camshaft. In this case, on the contrary, the insulation character of the linings 4 is reinforced to as much as a millimeter or more, by providing an extra thickness 10 of pasteboard, which also has the effect of protecting the casting from the nearby cooled zones 7. Still, the problem with this reinforced insulation is that the generation of gases is augmented which thereby risks producing blowholes. To overcome this, the die may be provided with filters 11 and air exhaust passages 12, according to a technique familiar in die casting, in order to facilitate the evacuation of these gases.

This local reinforcement in thickness of the pasteboard has in particular the advantage of permitting the casting of thin spiders of cast iron while retaining the gray structure for the cast iron. Thus, for example, one can readily cast pulleys having a massive hub and a massive rim joined by thin spiders.

Tests made with different types of cast iron, for forming camshafts and piston rings, have shown that with a thickness on the order to l millimeter of pasteboard, it is possible to cast thin sections of about 5 millimeters in thickness while retaining the structure of gray iron throughout, these values by no means constituting a limit. One can actually reduce the thickness of the thin section by increasing that of the pasteboard, and convcrsely.

It can be seen, therefore, that the method of the present invention is applicable to the fabrication of all sorts of castings, with particularly interesting and favorable results being shown in the case of items with variations in hardness, such as Camshafts and the like, where effective control of the tempered zones is obtained, something that is much more delicate to control in the classical techniques of casting in sand with suitable cooling. On the other hand, the method is perfectly applicable to the fabrication of all parts containing thin sections, such as suspension arms or steering gear housings for automobiles.

Obviously, many modifications and variations of the present invention are possible in light of these teachings. It is therefore to be understood that within the scope of the appended claims, the invention can be practiced otherwise than as specifically described herein.

What is claimed as new and desired to be secured by Letters Patent of the US. is:

l. A method of casting parts from metals having high melting points in molds, comprising the steps of:

prefabricating a form of a pasteboard material and containing a refractory substance in the shape of the cavity of each of the dies of the mold;

perforating at least one of said prefabricated pasteboard forms to produce at least one zone wherein more rapid cooling may take place;

placing each of said prefabricated pasteboard forms in the respective cavities of said dies of said mold; closing said dies of said mold to secure said pasteboard forms therein; and

filling the pasteboard covered cavities of said dies with a high melting point metal to cast said part. 2. A method of casting parts as set forth in claim 1, wherein said refractory substance is a layer thereof deposited on said prefabricated pasteboard forms by spraying.

3. A method of casting parts as set forth in claim 1, wherein said refractory substance is a layer thereof deposited on said prefabricated pasteboard forms by dipping.

4. A method of casting parts as set forth in claim 1, wherein said refractory substance contained in said prefabricated pasteboard forms is impregnated therein during the prefabrication thereof.

5. A method of casting parts as set forth in claim 1, further comprising providing a peripheral border on each of said pasteboard forms in the prefabrication thereof projecting outward in the plane of joining of said dies of said mold when they are closed, whereby said borders of said prefabricated pasteboard forms are clamped together in said joining plane to assure improved sealing of the interior of said mold.

6. A method of casting parts from metals having high melting points in molds, comprising the steps of:

prefabricating a form of a pasteboard material and containing a refractory substance in the shape of the cavity of each of the dies of the mold;

increasing the thickness of at least one of said prefabricated pasteboard forms in at least one selected local region to produce at least one zone wherein slower cooling occurs;

placing each of said prefabricated pasteboard forms in the respective cavities of said dies of said mold;

ping.

9. A method of casting parts as set forth in claim 6, wherein said refractory substance contained in said prefabricated pasteboard forms is impregnated therein during the prefabrication thereof.

10. A method of casting parts as set forth in claim 6, further comprising providing an air exhaust passage and a filter in each of said dies wherein the prefabricated pasteboard form therein is of increased thick 

1. A method of casting parts from metals having high melting points in molds, comprising the steps of: prefabricating a form of a pasteboard material and containing a refractory substance in the shape of the cavity of each of the dies of the mold; perforating at least one of said prefabricated pasteboard forms to produce at least one zone wherein more rapid cooling may take place; placing each of said prefabricated pasteboard forms in the respective cavities of said dies of said mold; closing said dies of said mold to secure said pasteboard forms therein; and filling the pasteboard covered cavities of said dies with a high melting point metal to cast said part.
 2. A method of casting parts as set forth in claim 1, wherein said refractory substance is a layer thereof deposited on said prefabricated pasteboard forms by spraying.
 3. A method of casting parts as set forth in claim 1, wherein said refractory substance is a layer thereof deposited on said prefabricated pasteboard forms by dipping.
 4. A method of casting parts as set forth in claim 1, wherein said refractory substance contained in said prefabricated pasteboard forms is impregnated therein during the prefabrication thereof.
 5. A method of casting parts as set forth in claim 1, further comprising providing a peripheral border on each of said pasteboard forms in the prefabrication thereof projecting outward in the plane of joining of said dies of said mold when they are closed, whereby said borders of said prefabricated pasteboard forms are clamped together in said joining plane to assure improved sealing of the interior of said mold.
 6. A method of casting parts from metals having high melting points in molds, comprising the steps of: prefabricating a form of a pasteboard material and containing a refractory substance in the shape of the cavity of each of the dies of the mold; increasing the thickness of at least one of said prefabricated pasteboard forms in at least one selected local region to produce at least one zone wherein slower cooling occurs; placing each of said prefabricated pasteboard forms in the respective cavities of said dies of said mold; closing said dies of said mold to secure said pasteboard forms therein; and filling the pasteboard covered cavities of said dies with a high melting point metal to cast said part.
 7. A method of casting parts as set forth in claim 6, wherein said refractory substance is a layer thereof deposited on said prefabricated pasteboard forms by spraying.
 8. A method of casting parts as set forth in claim 6, wherein said refractory substance is a layer thereof deposited on said prefabricated pasteboard forms by dipping.
 9. A method of casting parts as set forth in claim 6, wherein said refractory substance contained in said prefabricated pasteboard forms is impregnated therein during the prefabrication thereof.
 10. A method of casting parts as set forth in claim 6, further comprising providing an air exhaust passage and a filter in each of said dies wherein the prefabricated pasteboard form therein is of increased thickness. 